1. Field of the Invention
The present invention relates to a fluid. booster amplifier which stabilizes operation by providing a negative feedback arrangement responsive to back pressures in an exhaust conduit.
2. Description of the Prior Art
U.S. Pat. No. 4,481,967 shows a control circuit for a current to pressure converter in which a pilot pressure provides pneumatic signals to a fluid amplifier, which provides pressure for process control. The device disclosed in U.S. Pat. No. 4,481,967 has electronic feedback. In FIG. 1 of this patent, a pneumatic booster amplifier of conventional design is shown in block diagram form. A typical pneumatic booster amplifier provides a diaphragm responsive to the pilot pressure, which then in turn operates a valve arrangement to provide an output pressure that is a proportional to the pilot pressure at a balanced condition.
U.S. Pat. No. 4,325,399 also discloses a current to pressure converter and schematically illustrates a spool valve type pneumatic amplifier.
FIG. 1 of the drawings of this application illustrates a conventional prior art fluid amplifier. Problems arise with the conventional prior art amplifier as shown in FIG. 1, in that the control air supply is proportioned with a valve assembly between a supply and exhaust port. The amount the exhaust valve opens is dependent upon the position of a flexible diaphragm that is sensitive to a pilot pressure, for example, a pilot pressure developed by a nozzle illustrated in the patents mentioned above. As exhaust flow through the exhaust port increases and back pressure developes in the exhaust passageways, the exhaust control valve moves from the force developed by exhaust back pressure. This positive feedback makes the valve difficult to fine tune, and it tends to create instability in operation.
Another standard type pneumatic booster amplifier is shown in Van Nostrand Scientific Encyclopedia, Sixth Edition (1983), pp. 2265-2266, where a discussion of pneumatic controllers is given. Also, typical pneumatic booster amplifiers are shown in "Modern Control Engineering", (Ogata Prentice Hall, Inc. 1970) in Section 5.2, page 161.